A damper of the above kind is described in European published patent application No. EP 0 304 169A, and comprises two guide rings which are arranged on either side of a damper plate. Either the damper plate is, or the guide rings are, coupled with a hub, for rotation with the latter after an initial clearance has been taken up. The dry friction damping means are operatively connected between the damper plate and the guide rings. The viscous damping means is located outside the zone which is delimited by the guide rings, and is confined within a housing which consists of two portions which are arranged for rotational or angular movement with respect to each other.
Viscous damper means, for coupling in common rotation, are provided firstly between the hub and one of the two said portions of the viscous damper housing, and secondly between the other one of the viscous damper housing portions and that one of the two relatively rotatable coaxial parts of the damper that is not coupled with the hub for rotation with the latter. In this way, the viscous damping means forms, with its housing, a "cassette" which can be added to a torsion damper constructed from standard components.
In certain cases, it may be desired not to couple the viscous damping means in common rotation with the hub (or with an axial extension that is fixed with respect to the latter), in particular with a view to avoiding additional manufacturing and/or assembly operations, such as forming splines in the hub.